1. Field of the Invention
The present invention relates to standing seam metal roofs, and more particularly but not by way of limitation, to a roofing system based on roof demand and zone determination.
2. Discussion
Metal panels are common architectural features for a class of buildings commonly called pre-engineered buildings. The roofs of such buildings are usually made of metal panels that are mounted on, and cover up, the structural members of the building, which are usually purlins, the metal panels making up the external roof facade. The metal roof panels serve both as functional and as aesthetic features of such buildings.
Further, all roofs have multiple functional demands that such roofs must meet. To understand the scope of such demands, it should be noted that a roof function can be viewed as any one of a set of qualities or traits that are desirable or required for a roof in its particular location. A roof function is any requirement that a building code, regulatory agency, governing agency or authority, a specifier or a customer may demand, require, conceive or specify for the roof, or for any portion thereof. A demand is the particular level of performance required of a roof to meet its requirement for a particular function.
Within these parameters, xe2x80x9cdemand zonesxe2x80x9d are those areas of a roof that require or that perform different levels of the functional performance required of the whole. Also, a xe2x80x9cdemand zone quality levelxe2x80x9d is the level of quality that a specific demand zone should possess to meet the imposed qualify for the specific area or location of the roof. Of course, it will recognized that demand zones for various functions can coincide or overlap.
As one considers a roof in its multi-layered functional performance requirements, it will be appreciated that the quality required by a roof will vary from zone to zone over a range of quality levels for the type of roof being constructed. Within the scale of quality levels imposed on a particular roof design, and as used herein to describe the quality selection for a discrete zone, the term xe2x80x9cover qualified demand zonexe2x80x9d will mean that such zone has a level of performance that meets the design requirements of at least the next higher demand zone quality level imposed by the design requirements for the roof.
In describing the present invention, it is desirable to deal with the broader aspect of a roof zone, while at the same time, dealing with specific variants or attributes that are available to a designer to achieve the required performance level specified or required for any particular roof. Thus, the variant of panel to panel seaming is useful to illustrate one method available to the designer to optimize performance and cost effectiveness. Likewise, the variant of panel wind uplift resistance is useful to illustrate one method available to the designer to optimize performance and cost effectiveness of the performance of one roof function.
Broadly, a roof shelters the interior of a building from the natural elements of wind, sun, rain and snow, and with the building walls, encloses the building interior for environmental control. Numerous types of metal panel roofs have been utilized to resist these elements of nature while permitting the metal panels to face the constant demands imposed by their environment.
The purlin members supporting the metal roof panels are themselves typically supported by rafters that extend from the roof eaves to the ridge peak. The purlins serve as underlying cross members that are interconnected to extend the length of the building.
Metal roofs can be classified by the manner in which the side-adjacent and end-adjacent overlapping panels are sealed at joints. xe2x80x9cShed roofsxe2x80x9d are roofs that shed water and achieve water tightness because gravity pulls the water down and away from panel joints more effectively than wind or capillary action can propel water through the joints. On the other hand, xe2x80x9cgasket roofsxe2x80x9d are made watertight by gasket material disposed between the panel joints and secured in place by encapsulating pressure imposed against the gasket material. Generally, gasket roofs can be installed where the roof slope is down to about 1 to 48.
An environmental condition encountered by all roofs is the load imposed by ambient wind conditions. Wind passing over a roof peak often creates reduced pressure immediately above the roof, resulting in a pressure gradient on the panels, with lower pressure above the roof than below. This pressure gradient causes an uplift force on the metal roof panels, causing the panels to be pulled upwardly and away from the purlins. This often is the primary cause of failure for metal roofs.
There are a number of apparatuses that affect the quality of performance and that can be selectively varied by varying the specific configuration of the apparatus to achieve a desired performance level of metal roofs. This can be illustrated by considering the means by which standing seam roof panels can be joined together in their side to side, and end to end, arrangements and mounted to their underlying support structure. As known in the art, standing seam roof panels are designed to withstand environmental elements such as wind, snow and rain, and since a metal roof is essentially a large area heat sink continually exposed to atmospheric weather conditions, the standing seam panels must accommodate thermal expansion and contraction over a wide range of ambient temperature.
Standing seam roof panels have interlocking sidelap portions, a female sidelap portion of one panel engaging and locking with a male sidelap portion of a side-adjacent panel. As used herein, the term xe2x80x9cside-adjacentxe2x80x9d is meant to indicate that a first panel is disposed to lay along side, and adjacent to, a second panel on the roof. The female and male sidelap portions of the panels are elevated, or standing, to extend upwardly from a central flat or corrugated medial portion of the panels.
The metal panels are attached to the supporting purlins by clips that engage the standing seams, and by fasteners that penetrate and extend through the panels. The fasteners, sometimes referred to as through-fasteners, typically are sheet metal screws that extend through the medial portions of the panels to attach to the purlins, preventing differential movement between the panels and supporting purlins.
Clips are devices that connect the standing seam joints, that is, the interlocked standing sidelap portions, to the supporting purlins. Both fixed and sliding clips are utilized. Fixed clips are metal devices that attach to the underlying purlins and to the side-adjacent metal panel standing seams. Sliding clips, also referred to as floating clips, attach to the side-adjacent metal panels at the standing seams and to the underlying purlins while permitting a degree of differential movement between the panels and the purlins. The selection of the type and spacing of such clips has a pronounced effect on the performance of several of the roof functions, as well as affecting the cost, of metal roofs.
The interlocking engagement of the sidelaps of the metal panels provide functional requirements such as stiffness and strength to a flexible roof structure. The use of floating clips allows the roof structure to expand and contract as a function of the coefficient of thermal expansion of the panel material, and the temperature cycles of the roof panels.
Another apparatus or mechanism providing several variants that determine the performance quality of a metal roof is that of the type of seaming process selected to interlock and seam the side-adjacent, and end-adjacent, panels. Several types of seaming processes have been developed for interlocking the sidelaps of adjacently disposed panels. Most such seaming processes involve the operation of inelastically bending or rolling portions of the female sidelap and the male sidelap together. This inelastic or plastic deformation of the sidelap portions forms interlocked joints, or locks, of varying strength. That is, the interlocked sidelaps can be rolled multiple times so as to increase resistance to unfurling, and generally, the more times the interlocked sidelaps are rolled or plastically deformed, the more resistant the lock will be to unfurling. However, stronger locks are obtained by a corresponding increase in the cost of manpower and equipment to perform the bending or locking operation.
As noted above, for any given roof configuration and its supporting structure, the quality of a particular zone of a roof is often a function of several attributes, such as the type of seaming between side-adjacent panels, the clip attachment, frictional resistance to one side adjacent male sliding line with its corresponding female. With regard to the seaming attribute in a particular range or scale of quality, most would agree that a standing seam roof having the lowest quality on such scale of quality would be that roof having seam joints that are the weakest with respect to wind uplift and that are the least watertight. On the other end of such scale of quality, a standing seam roof having the highest quality would be the roof having seam joints that are the strongest with respect to wind uplift and are the most watertight.
In the art, sidelap seaming currently follows the practice of roll seaming adjacent sidelaps from one end of the panels to the other end of the interlocked panels. Only when the seaming machine malfunctions is this practice altered, in that the seaming machine is restarted at the point of malfunction and the seaming is completed as much as possible as though the malfunction had not occurred.
Many factors must be considered in the design and selection of a standing seam roof for a specific building. Of primary concern is the roof performance criteria, which may be determined by the geographic location of the building and the typical weather conditions expected during the life of the building. Modem day building codes impose many different requirements for the roof of a building. Codes include requirements for live loads, dead loads, snow loads, wind loads and earthquake loads.
Further, it is known that different areas or zones of the roofs typically are subjected to different loadings, especially with regard to wind uplift. Also, watertightness is often more critical in some areas than in others and is a major concern in valleys and other low spots.
The non-utilitarian, or aesthetic, aspect of metal roofs must also be considered, as roof appearance is often important when deciding the kind and amount of joint seaming that will be used to interlock the roof panels. Generally, roofs are more aesthetically pleasing when less elastic deforming is used at the panel sidelaps.
Considering these design factors, it has been the practice in most instances to determine the most critical portion of the roof and to require that all portions of the roof meet the design parameters of the most critical portion of the roof. The result of this approach is that the design specifications for the other less demanding portions of the roof exceed that which is necessary. This approach results in an unnecessary increase in the cost of the roof. Thus, there is a need for a roof that meets the requirements of all zones of all functions of the roof, minimizes the cost of the roof and is aesthetically acceptable.
The present invention provides a metal panel roof that uses different types of connecting processes as required to meet the demand requirements for the zones of performance demands for the completed roof.
A system is herein provided for constructing a roof on roof support structures which involves (a) identifying and mapping the roof by zones of demand requirements throughout the area to be covered by the roof, and (b) covering the area with metal panels or the like. It also involves the steps of choosing connecting processes for the side-adjacent and end-adjacent panels for all of the demand zones, with a zone specific connecting process selected for each demand zone and wherein the zone specific connecting process meets the performance criteria for that particular demand zone. Finally, the metal panels are inter-connected to each other and connected to the supporting roof support structures in each demand zone by the zone specific connecting process that meets all of the demand requirements for the demand zones. so that all of the metal panels are inter-connected to each other and to the roof support structure.
For example, a metal panel roof is zone mapped for performance requirements according to the functional performance required of its demand zones. The metal panels are attached to the underlying roof support structure and elastically seamed together by a roll-and-lock seam in accordance with a seaming type assigned to each zone. Next, the minimum quality of seaming is determined that meets the functional performance requirements of the multiple demand zones. Finally, the side-adjacent metal panels are seamed together by that seaming process that both meets the seam quality required for the demand zone and does so at the least cost. The end adjacent metal panels are also joined together so as to achieve consistent quality and cost as that of the side-adjacent seams.
The features, advantages and advantages of the present invention will be made apparent from the description provided herein below when read in conjunction with the accompanying drawings and claims.